Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Transmission-type holography techniques can be used to reproduce two-dimensional and three-dimensional images in a holographic television system. In such a holography television system, a hologram can be displayed on a high-definition liquid crystal display panel constituted of pixels having a resolution of the order of the optical diffraction limit The hologram may be formed based on fringe patterns contained in television image signals that can be transmitted through a television broadcast channel. In particular, the hologram can be formed using a reconstruction light (e.g., from a laser light source) that is irradiated from one side of the display panel on the fringe patterns displayed and arranged vertically with respect to the plane of the display panel. The irradiation of the reconstruction light on the fringe patterns causes diffraction in the fringe patterns, such that a user can observe the diffracted light as holographic images emitted from the other side of the display panel.
However, conventional transmission-type holography television systems may not be able to reproduce images in a realistic setting because the images are reproduced by the diffracted light emitted from the opposite side to the side of display panel on which the reconstruction light is incident. On the other hand, a human being can recognize a three-dimensional object by observing light reflected on the object, which is contrary to the above described conventional principles of transmission-type holography. Further, images reproduced in the transmission-type holography television system have a lower luminance compared to that of the display panel, which may deteriorate the visibility and distinction of the images viewed by the user. Furthermore, because a monochromic light such as laser light is typically used as the reconstruction light, the images may not be properly reproduced in color.
To resolve the above problems of the transmission-type holography, reflection-type holography techniques can be used in implementing a holography television system. In a reflection-type holography television system, hologram images can be formed based on multiple layers of fringe patterns displayed and arranged horizontally with respect to the plane of the display panel. A reconstruction light can be irradiated on the fringe patterns, which results in diffraction in the fringe patterns. In particular, in Lippmann holography, when a reconstruction light is irradiated on the fringe patterns, three-dimensional images can be reproduced through Bragg reflection. Bragg reflection refers to a phenomenon where light with particular wavelengths can be selectively reflected in response to the space between the fringe patterns and the orientation thereof, whereas light with the other wavelengths can be transmitted or absorbed into the recording medium in the display panel.
With the above-described characteristics, Lippmann holography may have various advantages including the capability of reproducing color images using white-color light. Also, Lippmann holography can provide clearer and brighter hologram images compared to conventional transmission-type holography because Lippmann holography has higher light diffraction efficiency. Further, since the hologram images can be reproduced by the reconstruction light selectively reflected on the fringe patterns, the user can observe the images as if the reproduced images are seen from a real world environment.
One example Lippmann holography television system may include a display panel with a transparent substrate including a two-dimensional matrix of small-sized optical elements and a controller that can individually provide control signals to the optical elements. When control signals are provided to the optical elements, the refractive index of the optical elements can change, which can cause a difference between the refractive indexes of the optical elements and the transparent substrate. In this configuration, wires are required to connect the controller to the optical elements in order to prevent leakage of the control signals. Such wiring may limit the reduction in the thickness of the display panel and also may interfere with the hologram images emitted from the optical elements. Another potential problem is that gaps between the optical elements may make it difficult to form continuous fringe patterns in the display panel.